The present invention is directed to cementitious dry cast mixtures, such as those for which vibration is used to consolidate and compact the dry cast mixture in a mold or extruder. Specifically, the invention is directed to the use of derivatized polycarboxylate additives that function at least in part as dispersants in cementitious dry cast mixtures to allow for reduced water usage, consolidation and compaction of the dry cast mixture, providing for increased compressive strength and reduced cycle time of dry cast formation. The invention is further directed to the use of derivatized polycarboxylate polymer dispersants in combination with surface active agents/air entraining agents to provide increased swipe and early compressive strength.
A cementitious dry cast mixture refers to pastes, mortars, and concrete compositions comprising a hydraulic cement binder having consistencies ranging from stiff to extremely dry as defined in ACI 211.3R, Table 2.3.1. Pastes are defined as mixtures composed of a hydraulic cement binder, either alone or in combination with pozzolans such as fly ash, silica fume, or blast furnace slag, and water. Mortars are defined as pastes that additionally include fine aggregate. Concretes additionally include coarse aggregate. These compositions may additionally include other admixtures such as set retarders, set accelerators, defoaming agents, air-entraining or air detraining agents, corrosion inhibitors, water reducing agents, pigments, and any other admixture that does not adversely affect the advantageous results obtained by the admixtures of the present invention.
Cementitious dry cast mixtures are used to form many articles, for example, concrete pipe, roof tile, masonry units, paver units, extruded plank, and any other preformed cementitious articles, in a mold or from an extrusion die. Each of these applications has basic desired characteristics that are critical in terms of producing quality finished units.
In masonry block applications, production speed, sufficient green strength, and the ability to resist slumping, sagging or deforming when stripped from the mold is critical since stripping occurs immediately after casting. The same is true for concrete pipe or roof tile with the additional desired property of improved surface appearance with reduced surface imperfections and reduced roller and/or die wear on equipment producing extruded pieces.
It is desired to reduce the cycle time of the manufacture of each article. The reduction of cycle time reduces the cost of manufacture for each article and increases the number of articles that can be produced in a given time. Cycle time is defined as the time to complete one full cycle from the beginning of feed to the end, or next beginning of feed. The beginning of feed is when the dry cast mixture is fed from a collection hopper into the process. It is also desired to improve the compaction and consolidation of the cementitious dry cast mixture without altering the consistency of the mixture.
Green strength refers to the stability of the article in retaining its shape once the article is removed from the mold or extruder. Green strength is dependent on the consistency of the cementitious dry cast mixture, the amount of fines in the cementitious dry cast mixture, and the moldability of the cementitious dry cast mixture.
Currently, the water to cement (W/C) ratio used in present dry cast mixtures is from about 0.25 to about 0.60. It is desired to minimize the amount of water needed in a cementitious dry cast mixture to achieve consolidation and no sag or deformation in an article produced from the cementitious dry cast mixture.
Another property of cementitious dry cast mixtures for certain dry cast industries is swipe. Swipe is defined as surface effect on a cast article when the mold is removed. Swipe is measured by visually evaluating the surface of the finished article. Swipe is ranked from no swipe to heavy swipe. It is desired to achieve a selected amount of swipe for a finished article.
A further limitation in the present art is the compressive strength of articles produced from cementitious dry cast mixtures. Early compressive strength is defined as the compressive strength achieved within 24 hours with or without steam cure. Compressive strength is determined by ASTM C-1176-2.
Another limiting factor in the improvement of dry cast mixtures is the type and amount of dispersant used. Conventional dispersant chemistries such as naphthalene sulfonates, melamine sulfonates, and lignosulfonates have a lower limit to their effective dosage; below which they are not effective. At levels above the effective dosage of these dispersants, the dry cast mixture becomes critically sensitive to very slight changes in water or moisture content. This makes the use of these dispersants impractical.
The art lacks a cementitious dry cast mixture containing a dispersant that has a low effective dosage, that is not critically sensitive to changes in water or moisture content, that functions in mixtures having a slump of less than about one (1) inch, that permits mixture consolidation and compaction in response to vibration energy, that has increased green strength and compressive strength, and that provides for reduced cycle time in the manufacture of articles from dry cast mixtures. The art also lacks a cementitious dry cast mixture containing a combination of a derivatized polycarboxylate dispersant with a surface active agent/air entraining agent to provide for increased swipe and increased early compressive strength.
It is an object of the invention to provide a combination of a derivatized polycarboxylate dispersant with a surface active agent/air entraining agent to increase the swipe and early compressive strength of a cementitious dry cast mixture.
It is another object of the invention to lower the effective dose of dispersant required to consolidate a cementitious dry cast mixture into the range of from about 0.005 to about 0.12% by weight of cement.
It is another object of the invention to provide a cementitious dry cast mixture article that has increased green strength and increased compressive strength.
The present invention is directed to cementitious dry cast mixtures for forming cementitious articles. In particular, the invention is directed to a cementitious dry cast mixture comprising cement, water, coarse aggregate, fine aggregate, and including a dispersant, wherein said dispersant is a derivatized polycarboxylate dispersant, or combination of polycarboxylate dispersants, which is a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer.
The present invention is also directed to a method for making a dry cast cementitious article comprising providing a mixture of hydraulic cement, water, coarse aggregate, fine aggregate, and including a dispersant, wherein said dispersant is a derivatized polycarboxylate dispersant which is a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer; and forming the article from the mixture.
The present invention is also directed to cementitious dry cast mixtures for forming cementitious articles. In particular, the invention is directed to a cementitious dry cast mixture comprising cement, water, coarse aggregate, fine aggregate, surface active agent/air entraining agent, and including a dispersant, wherein said dispersant is a derivatized polycarboxylate dispersant, or combination of polycarboxylate dispersants, which is a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer.
The present invention is also directed to a method for making a dry cast cementitious article comprising providing a mixture of hydraulic cement, water, coarse aggregate, fine aggregate, a surface active agent/air entraining agent, and including a dispersant, wherein said dispersant is a derivatized polycarboxylate dispersant which is a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer; and forming the article from the mixture.
The present invention concerns the use of low levels of derivatized polycarboxylate dispersants to improve the consolidation of cementitious dry cast mixtures. A derivatized polycarboxylate dispersant is defined as a polymer comprising units derived from at least a substituted carboxylic acid monomer or substituted ethylenically unsaturated monomer, and optionally including at least one of an unsaturated hydrocarbon, an N-polyoxyalkylene maleimide, and a condensation product of an unsubstituted carboxylic acid monomer and an alkoxypolyoxyalkylene primary amine substituted carboxylic acid monomer. The dispersant preferably has the general structure shown below: 
where:
D=a component selected from the group consisting of the structure d1, the structure d2, and mixtures thereof;
X=H, CH3, C2 to C6 Alkyl, Phenyl, Substituted Phenyl such as p-Methyl Phenyl, Sulfonated Phenyl;
Y=H, xe2x80x94COOM;
R=H, CH3;
Z =H, xe2x80x94SO3M, xe2x80x94PO3M, xe2x80x94COOM, xe2x80x94OR3, xe2x80x94COOR3, xe2x80x94CH2OR3, xe2x80x94CONHR3, xe2x80x94CONHC(CH3)2CH2SO3M, xe2x80x94COO(CHR4)nOH where n=about 2 to about 6;
R1, R2, R3, R5 are each independently xe2x80x94(CH2CHRO)mR4 random copolymer of oxyethylene units and oxypropylene units where m=about 10 to about 500 and wherein the amount of oxyethylene in the random copolymer is from about 60% to 100% and the amount of oxypropylene in the random copolymer is from 0% to about 40%;
R4=H, Methyl, C2 to about C6 Alkyl, about C6 to about C10 aryl;
M=H, Alkali Metal, Alkaline Earth Metal, Ammonia, Amine, Substituted Amine such as triethanol amine, Methyl, C2 to about C6 Alkyl;
a=0 to about 0.8, preferably 0 to about 0.6, and most preferably 0 to about 0.5;
b=about 0.2 to about 1.0, preferably about 0.3 to about 1.0, and most preferably about 0.4 to about 1.0;
c=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1;
d=0 to about 0.5, preferably 0 to about 0.3, and most preferably 0 to about 0.1; and
wherein a, b, c, and d represent the mole fraction of each unit and the sum of a, b, c, and d is 1.0.
Representative monomers for use in this invention for the xe2x80x9caxe2x80x9d component include, but are not limited to, styrene, ethylene, propylene, or sulfonated styrene. Representative monomers for use in this invention for the xe2x80x9cbxe2x80x9d component include, but are not limited to, acrylic acid, methacrylic acid, alkyl esters of acrylic acid, alkyl esters of methacrylic acid, alkoxypolyoxyalkylene esters of acrylic acid, aryloxypolyoxyalklyene esters of acrylic acid, alkoxypolyoxyalkylene esters of methacrylic acid, aryloxypolyoxyalkylene esters of methacrylic acid, maleic acid, vinyl sulfonic acid, methoxypolyoxyalkylene vinyl ether, methoxypolyoxyalkylene allyl ether, alkoxypolyoxyalkylene vinyl ether, aryloxypolyoxyalkylene vinyl ether, alkoxypolyoxyalkylene allyl ether, or aryloxypoloxyalkylene allyl ether.
Components xe2x80x9ccxe2x80x9d and xe2x80x9cdxe2x80x9d can be formed from a post reaction from the grafting of the side chains onto the polymer backbone such as a polyacrylate maleic anhydride copolymer. The reaction to form component xe2x80x9ccxe2x80x9d and/or xe2x80x9cdxe2x80x9d is related to the temperature of the grafting reaction. If the temperature is high enough, the imide components xe2x80x9ccxe2x80x9d and xe2x80x9cdxe2x80x9d are formed. Component xe2x80x9ccxe2x80x9d is formed from a single monomer which is a component xe2x80x9cbxe2x80x9d with Y as COOH and Z as CONHR3. A condensation reaction occurs wherein water condenses and the ring closes to form component xe2x80x9ccxe2x80x9d.
Component xe2x80x9cdxe2x80x9d is formed by a condensation of two monomers such as acrylic acid (component xe2x80x9cbxe2x80x9d with Y as COOH and Z as H) and an acrylic acid derivatized with an alkoxypolyoxyalkylne primary amine, that is a component xe2x80x9cbxe2x80x9d with Y as H and Z as CONHR3. A condensation reaction occurs wherein water condenses and the ring closes to form component xe2x80x9cd1xe2x80x9d or xe2x80x9cd2xe2x80x9d. Component xe2x80x9cd2xe2x80x9d is formed by a head to head reaction of the two monomers. Component xe2x80x9cd1xe2x80x9d is formed by a head to tail reaction of the two monomers.
In one preferred embodiment, components xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d are present and xe2x80x9ccxe2x80x9d and xe2x80x9cdxe2x80x9d are absent in the polymer of the derivatized polycarboxylate dispersant.
The alkali metal in the present invention is preferably lithium, sodium, or potassium. The alkaline earth metal in the present invention is preferably magnesium or calcium.
While polycarboxylate dispersants in general are known in the industry to be highly effective and efficient at producing highly flowable concrete, the derivatized polycarboxylate dispersants of the present invention may be advantageously used at low to extremely low levels, 0.005 to 0.12% by weight of cement, to improve the paste phase response to vibration or other energy applied to the cementitious dry cast mixture during consolidation. Consolidation and compaction of the dry cast mixture results in increased compressive strengths, higher density, lower water absorption or permeability, and better surface appearance of the finished unit (reduced imperfections and holes). Additionally, the reduced levels of dispersants result in a reduced cost for materials for the cementitious dry cast mixture.
Cementitious dry cast mixtures of the present invention generally comprise hydraulic cement, the dispersant, fine aggregate, coarse aggregate, and optionally silica fume, pozzolans such as fly ash or calcined clay, and pigments. Water is added to form the cementitious mixture into a paste.
The hydraulic cement can be a portland cement, a magnesium phosphate cement, a magnesium potassium phosphate cement, or any other suitable hydraulic binder. The coarse aggregate can be silica, quartz, crushed round marble, glass spheres, granite, limestone, calcite, feldspar, alluvial sands, any other durable aggregate, and mixtures thereof. The fine aggregate can be sand, any other suitable aggregate, and mixtures thereof.
Cementitious dry cast mixtures have been found to respond to vibration or applied energy when the mixture is properly proportioned. The derivatized polycarboxylate dispersants improve the mobility of the paste when under stress from vibration or energy. When the mold is subjected to vibration or other energy, the paste fraction of the mixture functions as the vehicle/lubricant by which the solid aggregate particles move and orient themselves during consolidation.
The derivatized polycarboxylate dispersants of the present invention allow for reduced water content, minimize the effect of the variation in size of the aggregate particles, and allow the incorporation of additional fines such as fumed silica in the mixture. All of these factors in turn improve the green strength of the articles formed from cementitious dry cast mixtures.
The reduced water content provides cementitious dry cast mixtures with stiff to extremely dry consistencies, with typical W/C ratios at or below 0.36, preferably at or below 0.30. Without being limited by theory, it is theorized that the reduced water content allows the cementitious dry cast mixture to hydrate and set faster which increases the green strength of an article formed from the cementitious dry cast mixture. This is also thought to result in reduced sagging and deformation when the article is removed from a mold or is extruded from a die. Additionally, the cementitious dry cast mixtures of the present invention have the appearance of dry to almost dry.
The derivatized polycarboxylate dispersants of the present invention minimize the effect of the variation in size of the aggregate particles by improving the lubricity of the thin paste layer covering the aggregate allowing improved movement during consolidation. This effect is typically obtained by increasing the cement content, the water content, or both. Minimizing water content and maximizing cement efficiency in turn increases the green strength of an article formed from the cementitious dry cast mixture.
Addition of silica fume increases the cohesiveness of the cementitious dry cast mixture which then increases the green strength of an article formed from the cementitious dry cast mixture. Silica fume used in the present invention can be uncompacted or can be partially compacted. Silica fume additionally reacts with the hydration byproducts of the cement binder which provides for increased strength of the finished articles and decreases the permeability of the finished articles. The silica fume, or other pozzolans such as fly ash or calcined clay such as metakaolin, can be added to the cementitious dry cast mixture in an amount from about 5% to about 30% based on the weight of cement.
By allowing for a reduced W/C ratio, improved paste lubricity and increased green strength, the cycle time of producing an individual article from a cementitious dry cast mixture is reduced. Compared to dry cast mixtures of the prior art, cycle time reductions are improved by 50 to 100%. By allowing articles to be removed from the molds in a shorter period of time or by increasing the rate of extrusion, the cycle time for producing each article is reduced. Additionally, more articles can now be produced in the same equipment. These factors combine to reduce the cost of manufacture of each article, such as masonry blocks.
Additionally, the additive dosage of the derivatized polycarboxylate dispersant of the present invention can be slightly increased (but still in the range of 0.005 to 0.12% by cement weight) in combination with a reduction of the W/C ratio to provide further improvements without changing the dry consistency of the mixture. As the dispersant level is increased, the W/C ratio can be decreased. The W/C ratio and dispersant level can be varied to optimize the production of each type of dry cast article from a cementitious dry cast mixture.
For masonry block, the compacted density and compressive strength of dry cast concrete mixtures have been shown to be increased over a plain reference at the same W/C ratio by using a derivatized polycarboxylate additive at about 0.01 to about 0.03% by weight of cement. The compaction speed, consolidation and resulting compressive strength of masonry block has been shown to be improved by using a derivatized polycarboxylate additive, most preferably at about 0.03% by weight of cement. The compressive strength of a dry cast mixture of the present invention is increased by up to 30%. The basic desired characteristics of the dry cast mixture for masonry block, which are sharp corners, sharp edges, no web cracking, no sagging or deformation, are not negatively affected by these improvements.
For pipe and roof tile, the increased density and compaction of the cementitious dry cast mixture additionally results in reduced imperfections in an article produced from the cementitious dry cast mixture. Typically, a cementitious dry cast mixture has air pockets that are retained in the mixture after the mixture has set. On the surface of an article, these holes are called bugholes and they detract from the aesthetic value of the article. Other imperfections referred to as honeycombs, which are zones of poorly compacted mixture, decrease the compressive strength of the article and increase the permeability of the article. The increased density and compaction, according to the invention, reduce or eliminate these problems. Additionally, other surface defects are eliminated by the vibratory consolidation of the cementitious dry cast mixtures of the present invention.
The derivatized polycarboxylate additive can be combined with other chemical or mineral additives typically used in the various applications such as set accelerators, set retarders, defoaming agents, air-entraining or air detraining agents, water repellant agents, water reducing agents, and any other conventional additives for cementitious mixtures. The basic properties of a cementitious dry cast mixture are not negatively affected by the use of the derivatized polycarboxylate dispersants of the present invention.
The polymers used in the derivatized polycarboxylate dispersant of the present invention can be made by methods known in the art, such as those referenced in U.S. Pat. No. 5,661,206 to Tanaka et al., U.S. Pat. No. 5,393,343 to Darwin et al., U.S. Pat. No. 5,158,996 to Valenti, U.S. Pat. No. 5,047,087 to Montague et al., U.S. Pat. No. 4,972,025 to Tsubakimoto et al., U.S. Pat. No. 4,968,734 to Gaidis et al., U.S. Pat. No. 4,473,406 to Bradley et al., and U.S. Pat. No. 4,471,100 to Tsubakimoto et al. all of which are hereby incorporated by reference herein as if fully written out below.
Another embodiment of the invention provides for a method for making a dry cast cementitious article. The method comprises providing a mixture of hydraulic cement, water, coarse aggregate, fine aggregate, and the above derivatized polycarboxylate dispersant, then forming the article from the mixture. Forming can be any method including placing the mixture in a mold and vibrating the mold or extruding the mixture through a die.
In another embodiment, the present invention provides for a combination of the above derivatized polycarboxylate dispersant with a surface active agent/air entraining agent. The combination provides for increased swipe and increased early strength.
The surface active agent/air entraining agent of the present invention can be any known surface active agents/air entraining agents for cement including anionic, cationic, nonionic surfactants, natural resin, synthetic resin, natural rosin, synthetic rosin, any inorganic air entraining agent, and mixtures thereof.
Illustrative examples of surface active agent/air entraining agents that can be used with the present invention include, but are not limited to, alkanolamides, alkanolamines, alkylaryl sulfonates, polyethylene oxide-polypropylene oxide block copolymers, alkylphenol ethoxylates, carboxylates of fatty acids, ethoxylates of fatty acids, sulfonates of fatty acids, sulfates of fatty acids, fluorocarbon containing surfactants, silicon containing surfactants, olefin sulfonates, olefin sulfates, and mixtures thereof. A preferred foaming agent is ethoxylated nonylphenol.
The foaming agent is added in an amount from about 0.001% to about 0.4% based on the weight of cement, preferably about 0.005% to about 0.012%.
Alkanolamide foaming agents according to the present invention include, but are not limited to, those having from about 12 to about 20 carbon atoms
Alkanolamine foaming agents according to the present invention include, but are not limited to, those having from about 12 to about 20 carbon atoms.
Alkylaryl sulfonate foaming agents according to the present invention include, but are not limited to, those having one aryl group and having alkyl groups with about 12 to about 20 carbon atoms.
Polyethylene oxide-polypropylene oxide block copolymer foaming agents according to the present invention include, but are not limited to, those having about 4 to about 50 units of each block.
Alkylphenol ethoxylate foaming agents according to the present invention include, but are not limited to, those having an alkyl group of about 4 to about 50 carbon atoms.
Carboxylates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the fatty acid moiety has about 6 to about 20 carbon atoms.
Ethoxylates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the number of ethoxylate groups is about 4 to about 20 and the fatty acid moiety has about 6 to 20 carbon atoms.
Sulfonates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the fatty acid moiety has about 6 to about 20 carbon atoms.
Sulfates of fatty acid foaming agents according to the present invention include, but are not limited to, those in which the fatty acid moiety has about 6 to about 20 carbon atoms.
Fluorocarbon containing surfactant foaming agents according to the present invention include, but are not limited to, those having about 6 to about 20 carbon atoms and one or more CH2 moieties are replaced by CF2 moieties.
Olefin sulfonate foaming agents according to the present invention include, but are not limited to, those having about 12 to about 20 carbon atoms.
Olefin sulfate foaming agents according to the present invention include, but are not limited to, those having about 12 to about 20 carbon atoms.
Representative examples of surfactant that can be used as the surface active agent/air entraining agent include ethoxylated nonylphenol, alpha olefin sulfonate, or cocamide DEA.
The derivatized polycarboxylate dispersant to surface active agent/air entraining agent ratio is from about 10:1 to about 1:10 by weight. Preferably, the ratio of the derivatized polycarboxylate dispersant to the surface active agent/air entraining agent is from about 6:4 to about 4:6 by weight.
Another embodiment of the invention provides for a method for making a dry cast cementitious article. The method comprises providing a mixture of hydraulic cement, water, coarse aggregate, fine aggregate, surface active agent/air entraining agent, and the above derivatized polycarboxylate dispersant, then forming the article from the mixture. Forming can be any method including placing the mixture in a mold and vibrating the mold or extruding the mixture through a die.